Question about the Room of Requirement

[demetra1225]

No: HPFGUIDX 137703

The Lexicon describes the Room of Requirement as a magical room which 
can only be discovered by someone who is in need.  The room will 
appear when someone walks past the wall three times while 
concentrating on what they need. 

We know that in OotP, The DA used the room for meetings.  The room 
stocked itself with useful books and objects one would use for DADA 
lessons.  
In OotP, Chapter 27, the Inquisitorial Squad discovered the DA had 
been using the room.  They found the room and the list of all of the 
members hanging on the wall.  I recall some theories that because the 
I.S. needed some evidence against the DA, the room provided it for 
them.

However, in Chapter 21 of HPB, we see Harry trying to get the room to 
appear to show him what Draco was up to.  The door to the room never 
appears.  

Why doesn't the room give Harry what he needs?  Was what he requested 
not specific enough?  Is it because Harry didn't *need* to know what 
Draco was up to, he only *wants* to know?  
Or does the room not allow people to see what other's are using it 
for?  But if that is the case, why did the room allow the I.S. to see 
what the DA was up to, but not allow Harry to see what Draco was up 
to?   

Any thoughts?

Demetra